Morgan Harper has been given first crack at replacing Tom Trbojevic after being named at fullback for Manly's NRL trial on Sunday.

The 22-year-old played just four NRL games at centre for the Sea Eagles last season but will state his case for Trbojevic's No.1 jersey in the final trial before the season starts on March 11.

Trbojevic is expected to miss at least the first three rounds of the season after suffering his fourth hamstring injury in two years.

It's forced coach Des Hasler to lean on the depth in his squad, with Harper and Reuben Garrick likely to both spend time at the back in Sunday's trial.

Winger Garrick filled in for two matches at fullback while Trbojevic was sidelined last season, but regular replacement Brendan Elliot was not re-signed by the club at the end of the year.

Meanwhile, Hasler has not named big-name stars Jake Trbojevic, Kieran Foran and Daly Cherry-Evans to face Wests Tigers at Leichhardt Oval on Sunday.

Cade Cust has been named at hooker ahead of Lachlan Croker, who is also being considered for the No.9 role but has not been named.